Conductive but Poor Metallic Solid Hydrogen

Hydrogen, the most abundant and lightest element in the universe, is the object of fundamental physics research focusing on its transition to a metallic phase. For decades, it has been predicted that metallization in pure hydrogen gives rise to superconductivity with very high transition temperature.

Recently, the existence of metallic solid hydrogen has been reported around 260 GPa, but results of more recent experiments are inconsistent with transition pressure. Rigorous theoretical work will aid our understanding of physical properties of solid hydrogen under pressure. In a study by EFree Director Ho-kwang Mao (Carngie) and colleagues from Carnegie, Nancy Université, Uppsala University, and the Swedish Royal Istitute of Technology, several computational techniques were used. The researchers predict that solid hydrogen becomes semi-metallic at 260 GPa and low temperature. Under those conditions, the superconductivity transition temperature is near 0.

The study predicted that insulating solid hydrogen will undergo a phase transition to a poor metallic state at low temperature. This suggestion indicates that conductance changes at the transition would be smooth than sharp. Alkali-type metallic phase of solid hydrogen would require much higher pressure than tested in our study [S. Lebègue et al. Proc. Nat. Acad. Sci. 108, 9766 (2012)].